Advertisement

Advertisement

Devastating El Niño events to double this century

By Michael Slezak

EXTREME El Niños, which can kill tens of thousands of people, will be twice as common this century – all because of climate change.

The El Niño Southern Oscillation (ENSO) has a dramatic effect on the weather. An El Niño happens when warm water spreads east across the Pacific, pushing rainfall with it to cause floods in the Americas and drought in Australia. Africa can also be hit.

Despite ENSO’s influence, until recently we had no idea whether climate change would make a difference to it, since climate models disagree on whether temperatures in the Pacific will vary more in future.

So Wenju Cai of the CSIRO in Melbourne, Australia, and colleagues took a different tack. They defined extreme El Niños according to their impacts on weather, rather than the changes in sea temperature. “What is really important is the rainfall,” says Dietmar Dommenget of Monash University, also in Melbourne.

Advertisement

Defining an extreme El Niño as one where usually dry regions in South America experience a tenfold increase in rain, they found that climate models do agree after all. Models suggest that extreme El Niños should now be twice as common&colon; about one a decade from 1990 to 2090. In the previous 100 years it was once every 20 years (Nature Climate Change, doi.org/q4c).

That’s because the eastern Pacific is warming faster than the west, so peak temperatures will happen more often in the east, shifting rainfall.

It is not clear if climate change has contributed to recent El Niños, but the cycle seems to be changing. Last year researchers reconstructed how ENSO had altered since 1590, and found it was more intense between 1979 and 2009 than at any earlier time (Climate of the Past, doi.org/q28).

Another recent study showed that even normal El Niños will bring more severe drought and rain (Nature, doi.org/n9n).

This article appeared in print under the headline “Devastating El Niños to double this century”